Nor is she troubled by the Harry Potter tag. "I'm still thrilled. I think if I was a Rada graduate and I was just an actress and acting was my life, I would be a bit more eager for people to notice me for other things." She still keeps up with Potter pals Evanna Lynch and Anna Shaffer, aka Luna Lovegood and Romilda Vane.

And she bumped into Daniel Radcliffe a couple of years ago in Soho. He didn't recognise her at first and his bodyguards thought she must be a crazed fan. "I just felt very sorry for him. It made a situation that was really normal – bumping into someone you've worked with – into something slightly formal."

She now has three more books in the works, including one about babies, and is in development with Channel 4 on a teen drama about a girl roller derby champion. She would like to do a chick-lit novel "with cartoons" and one day maybe make a British Daria or Family Guy.

"I'm ridiculously ambitious and eager to share things I've made myself. As an actress I'm aware of the realities of the business. I understand that I might never work again. And that's OK, really," she says, strapping Donnie in again. "If I hadn't got Harry Potter, I don't know how things would have turned out... but I feel like I'm now in the right place."